The role of the contingent negative variation in chunking. Evidence from a go/nogo discrete sequence production task.

In the present EEG study we examined the effect of differing lengths and complexities of learned motor chunks on the contingent negative variation (CNV). Participants learned two different three-key sequences (A and B/1x3 sequence) in a go/nogo discrete sequence production (DSP) task in the practice phase. In the test phase, the two sequences had to be executed in combinations of two (with four possible combinations, either two times the same sequence, AA or BB/2x3 sequences, or different sequences in succession, AB or BA/1x6 sequences). We hypothesized that the CNV would be more negative for the more complex (1x6) than for the less complex (2x3) sequences and more negative for the long (1x6 and 2x3) comparead to the short (1x3) sequences. Comparisons were thus made between execution of the 2x3 (less complex) versus the 1x6 (more complex) sequences and between execution of the short (1x3) versus the long (2x3 and 1x6) sequences. The effects on the CNV were assessed with regard to amplitude at three different electrode locations (Fz, Cz and Pz). The results revealed that with the exception of interaction effects, which indicated that only at Pz negativity was more pronounced for long than for short sequences, differences in CNV response of none of the other comparisons were significant in the direction of our hypotheses. We concluded that the results were probably due to either the present application of particular assumptions about the CNV or to differential task demands in the practice and the test phase resulting in different kinds of motor preparation, which made comparison of both unfeasible. Furthermore, concurrent processing might have proceeded during execution of the response, which means that the CNV as indication of motor preparation might have been incomplete. Most likely, due to the bad spatial resolution of EEG measurement, the CNV could only be found to reveal differences at Pz, although differences do exist at other locations, as well. It might also have been that our intended effect is only visible at Pz for some unknown reasons. Clearly, more research is needed in order to disentangle the complex relationships between chunking, motor preparation, and the CNV.